This invention relates generally to plastic beverage containers and more particularly to an improved container comprising a blow molded bottle with a stabilizing ring attached to the base of the bottle extending radially outwardly and downwardly to increase the vertical stability of the container when supported upright on a horizontal surface. By vertical stability is meant the ability of the container to resist tipping over from its upright position. Resistance to tipping is important for both empty and full containers being handled by automatic equipment or by individual people.
A major difficulty with the use of plastic bottles for carbonated beverages is in providing sufficient strength to the base of the bottle to prevent undesirable deformation. Due to internal carbonation pressures in the bottle which can exceed 75 psi, plastic bottles can deform in the base structure resulting in a bottle which will not stand upright on a flat surface. In addition, when the base deforms, the volume of the bottle typically increases, thereby lowering the fill line of the bottle such that potential consumers may believe that the bottle was not properly filled or sealed.
One solution to the problem of base deformation is to provide a bottle having a hemispherical base extending downward from the lower end of the sidewall. A second piece, commonly known as a base cup, is attached to the hemispherical base to provide stability. The base cup includes a generally flat bottom and an upstanding cylindrical wall extending upwardly from the periphery of the bottom and engages the side of the bottle. This type of container is commonly referred to as a composite container and is widely used for carbonated beverage containers of sixteen ounces or more.
The disadvantages of a composite container include increased material cost and weight. Base cups are often made of polyethylene which has dramatically increased in cost. The base cup contributes approximately one-third of the container weight while contributing almost one-half of the material cost.
To overcome the disadvantages of a composite container, one-piece bottles have been developed with reinforced base structures. The plastic material in the base is greater than the bottle base of a composite container but the total one-piece container weighs less than the composite container including the base cup.
A one piece plastic bottle is disclosed in U.S. Pat. No. 3,598,270 to Adomaitis et al which is typically used for containers having a capacity of two liters. The base of this bottle has a hemispherical bottom wall with a plurality of hollow legs extending downwardly from the bottom wall. However, it can be difficult to consistently mold this bottle with the plastic being properly molded in the bottom of the hollow legs to form a horizontal supporting surface for the bottle.
For small containers with a capacity of sixteen ounces, another base configuration for a one-piece bottle is disclosed in U.S. Pat. No. 4,334,627. The base of this bottle has a central recessed portion forming a dome which extends upwardly into the bottle similar to a champagne bottle base. A number of radially extending solid ribs are molded onto the inner surface of the base to provide added strength to prevent deformation of the base. It is difficult, however, to make this bottle having a capacity larger than sixteen ounces with sufficient strength in the base. As the capacity of the bottle is increased, the diameter of the central recess also increases, increasing the reinforcement needed in the base.
Accordingly, it is an object of the present invention to provide a container that is economically and consistently blow molded, that has a base structure resistant to deformation caused by internal pressures and that has vertical stability equal to or better than the prior art containers.
It has been discovered that a plastic container having a central recessed dome in the base can be made with sufficient strength to prevent undesirable deformation, without the internal ribs shown in U.S. Pat. No. 4,334,627, if the diameter of the dome is sufficiently small. The outer periphery of the dome portion of the container forms an annular heel which functions as a support surface for the container. By reducing the size of the dome to increase its strength, the diameter of the heel is also reduced. This in turn reduces the vertical stability of the container
To increase the vertical stability of the container, a separate stabilizing ring is attached to the base structure which extends radially outwardly and downwardly to form a container support of increased diameter.
Further objects, features and advantages of the invention will become apparent from a consideration of the following description and the appended claims when taken in connection with the accompanying drawings.